Answer:
Option C) Type I error
Explanation:
We are given the following in the question:

Type I error:
- It is also known as false positive.
- It is the rejection of a true null hypothesis.
Type II error:
- It is known as false positive.
- It is the acceptance of a false alternate hypothesis.
An incoming legitimate message is flagged spam by a spam filter.
Thus, a true null hypothesis that the message is legitimate is rejected and the message is send to spam folder.
Thus, spam filter made a
Option C) Type I error